Very high efficiency hybrid steam/gas turbine power plant wiht bottoming vapor rankine cycle

Abstract

An improved thermal efficiency power plant for converting fuel energy to shaft horsepower is described. The conventional combustor of a gas tubine power plant is replaced by a direct contact steam boiler 8, modified to produce a mixture of superheated steam and combustion gases. Combustion takes place preferably at stoichiometric conditions. The maximum thermal efficiency of the disclosed plant is achievable at much higher pressures than conventional gas turbines. Uses of multi-stage compression turbines (4, 9, 1, 10) with intercooling (2, 3) and regeneration (16, 17, 18, 19) is utilized along with a vapor bottoming cycle (11, 12, 13) to achieve a thermal efficiency greater tha 60% with a maximum drive turbine inlet temperature of 1600 degrees Fahrenheit.

Description

BRIEF DESCRIPTION OF DRAWINGS

Other objects and advantages of the invention will become apparent upon reading the following detailed description of and upon reference to the drawings in which:

FIG. 1 is a semi-schematic block diagram of a preferred embodiment i.e., a power plant incorporating principles of the disclosed invention typical but not limiting temperatures, pressures, flow and heat rates are shown.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The basic cycle is diagrammed in FIG. 2. The unit can be of any size. Other arrangments can be chosen to give optimum operating conditions according to the desired application. We shall use as an operating example the power plant having parameters shown as Example 1 where the detailed flow rates and thermodynamic properties given. The maximum temperature is chosen as 1600.degree. F. in order to utilize state of the art gas turbine technology. Example 1 is a specification sheet and description of a power plant constructed according to the principles of the invention, particularly showing typical performance data of various components such as fluid pressures, temperatures and flow rates.

With particular reference to FIG. 1, there is shown a turbine driven power plant suitable for driving an electric generator or providing shaft horsepower for other requirements. As disclosed, the system utilizes a main drive turbine 9 providing shaft horsepower to a load 20, typically a dynamo electric generator. An axial or centrifugal compressor 4 is mechanically coupled to the drive turbine 9 for delivering combustion air at pressures and temperatures in the range of 1500-3000 PSIG and 700.degree. F., to a direct fired steam generator 8 of the type disclosed in U.S. Pat. No. 4,490,542. The steam generator is also supplied with feedwater at a temperature in the range of 700.degree. F. at 8A, and fuel at its inlet 8B. Combustion air and fuel are contacted within the generator such that combustion is essentially complete prior to the injection of the feedwater.

As shown, the direct fired steam generator ouput consisting of steam and combustion products enter the drive turbine 9 at pressures in the pressure and temperature ranges of 3500 lbs. per square inch and 1600.degree. F. respectively. Drive turbine 9 is of the axially stages type having a plurality of operating fluid discharges at 9a, 9b, 9c and 9d. The function and use of these discharges will be fully developed below.

An additional and auxiliary compressor/turbine is comprised of expansion turbine 10 operating from drive turbine exhaust 9a. A steam generator combustion air compressor 1 is mechanically coupled to the expansion turbine 10 for raising atmospheric inlet air entering the turbine at 1a thereby providing combustion air temperatures and pressures in the range of 800.degree. F. and 235 PSIA as a pressure boosted supply at the inlet of feedwater and Freon heat recovery exchangers 2, and 3 respectively. Combustion air cooled to 60.degree. F. and 225 PSIA, exiting exchanger 3, enter the low pressure inlet of compressor 4. The high pressure output of compressor 4 supplies combustion air to the direct fired generator 8 at inlet 8c.

In keeping with a major concept of the invention disclosed here, i.e., a Freon bottoming cycle which will be discussed in detail below, including Freon heat exchanger 3, is utilized to cool exit air from first stage combustion air compressor 1 thus reducing the power requirement of the combustion air compressor 4. Typically, as shown, inlet air to the combustion air compressor 4 is cooled from 220.degree. F. to 60.degree. F. at the inlet of compressor 4. Similarly, a feedwater heater 2 is also utilized to cool the combustion air delivered to combustion air compressor 4 as shown on FIG. 1.

With further reference to the above mentioned Freon bottoming cycle, the expansion turbine 10 operating from exhaust tap 9a of the drive turbine 9, separates the exhaust products into noncondensing gases exiting at 25, with water vapor, from direct fired steam generator exhaust exiting at outlet 22. The bottoming cycle Freon boiler and exhaust condenser 11 is supplied from expansion turbine 10, at its exit 22, wherein heat is extracted from a Freon boiler or heat exchanger 26 for driving the Freon expansion turbine 12. Expansion turbine 12 therefore, operates from Freon vapor exiting the Freon boiler at 23, typically at temperatures in the range of 238.degree. F.

The Freon expansion turbine 12 can be used to drive an auxiliary generator or provide other shaft horsepower as shown at 22. Freon vapors exiting the expansion turbine 12 at 24 are condensed to liquid Freon in the Freon condenser 13 and enter Freon pump 14 driven by an external source of energy 20 for delivery to a Freon/combustion air cooler 3, for further decreasing the power requirement of the combustion air compressor 4.

The use of more than one compressor for supplying combustion air is a necessary teaching of the invention disclosed for the following reason; Since the optimum pressure ratio of this cycle is quite high, if only one compressor is used, the temperature of the air leaving the compressor could be higher than the maximum cycle temperature. This would be undesirable from the point of view of the cycle efficiency as well as the blade material of the compressor. However, the optimum number of compressors and their individual pressure ratio is dependent on the power plant design and those knowledgeable in the art would have no difficulty in making the choice.

The amount of fuel and air supplied to the boiler 8 is regulated in such a manner that the temperature leaving the direct contact boiler 8 is the maximum temperature desired for the operation of the power plant. The direct contact boiler could be designed in two stages if necessary.

The hot Vapor and combustion gases leaving the direct contact boiler 8 expand through turbine 9 adiabatically. In this particular embodiment the turbine 9 drives compressor 4 as well as a load 20. Also the turbine 9 has three bleed points that supply hot gases to the three regenerative heat exchangers 17, 18 and 19 as discussed above. Typically, in keeping with Applicant's invention, feedwater temperatures and exchangers 16, 17, 18 and 19 are limited to saturation values at specific pressures of their inputs from the respective drive turbine discharge outlets 9a, 9b, 9c, and 9d respectively. Under these operating conditions of pressure and temperature, the temperature difference between drive turbine exhaust products and feedwater undergoing heating is maximized, thereby avoiding the "pinch point" limitation found in prior art regenerative heat recovery as discussed above (Reference FIG. 1, and FIG. 2-paragraph 5).

The drive turbine exhaust gases leaving the turbine 9, at 9a expand adiabatically through the turbine 10 which drive the compressor 1 and the load 21. The turbine 10 has one bleed point, 10a, supplying hot gases to the regenerative heat exchanger 16 for heating feedwater and Freon in exchangers 16 and 26 respectively. The number of turbines and their arrangement in this embodiment is not a critical part of the invention disclosed as indicated above. Other arrangements could be more efficient or desirable depending on the power plant and specific application or use.

Exhaust gases leaving the turbine 10 enter the boiler condenser 11. Freon 11 cools the exhaust gates in the boiler condenser 11 thus condensing most of the water present. The non-condensable gases are discharged to the atmosphere through outlet 25 and the excess water resulting from the combustion of the fuel, through outlet 21. The feed water leaving the boiler condenser 11 via outlet 20 is pumped by pump 15 as described above, through the various regenerative heaters and the compressor intercoolers and returned to the direct contact steam generator 8.

Vaporized Freon 11 leaving the boiler condenser 11 at point 23, expands adiabatically through the turbine 12 which drives an auxiliary load 22. The Freon 24 leaving the turbine 12 is condensed in a condenser 13 and then pumped by pump 14 through the compressor intercooler 3 and then returned to condenser and Freon boiler 11. The bottoming cycle characteristics as utilized in this invention used Freon 11 or any suitable fluid is a necessary condition for the operation of the power plant at greatly increased efficiencies.

As indicated by Example 1, the preferred embodiment of the invention disclosed provides a means for increasing the efficiency of a Brayton cycle turbine through increased high-pressure injection of steam and combustion products as discharged from a direct fired steam generator of known design. The system disclosed provides both high pressure combustion air from compressors 1 and 4, and feedwater from pump is for the high pressure steam generating system.

This application of the direct fired steam generator, in addition to improving the Grayton cycle efficiency, allows the use of high pressure combustion techniques developed elsewhere to produce a small lightweight highly reliable power generating system wherein the turbine inlet temperature and pressure can be readily controlled through control of the direct fired steam generator discharge.

As indicated by Example 1, overall turbine compression ratios of the system disclosed in approximately 200, while the gas turbine inlet temperatures do not exceed 1600 degrees Fahrenheit. It should be noted, present turbine technology provides at moderate cost the equipment which reliably operates at the 1600 degree figure.

EXAMPLE 1

1. Two stage compressors (i.e., #1 and #10; #4 and #9) with a pressure ratio of 16:1 each.

2. A direct fired steam generator (DFSG) #8 operating with stoichiometic air-fuel ratio and using fuel with lower heating value of 19300 BTU/LB.

3. Two inter-stage air coolers (i.e., #2, and #3).

4. Four regenerative heat exchangers (16, 17, 18, and 19).

5. A bottoming Freon-11 Rankine cycle (11, 12, and 13).

6. Atmospheric pressure is 14.7 psia at 60.degree. F.

7. Heat rejection temperature is 60.degree. F.

8. Compressor efficiency of 85% and turbine efficiency of 90%.

9. Feedwater supplied to the direct contact boiler (#8) at 700.degree. F.

Considering a flow of air of 1 lb/sec, the following calculations are determined:

1. The air leaves the first stage compressor 1 at 235 psia and 800.degree. F. The power requirement of this compressor stage is 254 hp/lb air/sec.

2. The air is cooled to 60.degree. F. after passing through two heat exchangers (2, 3), one using water and the second using Freon-11 as heat exchange medium. A 10 psia pressure loss in the two exchangers is considered.

3. The air leaves the second stage compressor 4 at 3600 psia and 800.degree. F. The power requirement of this second stage compressor is 254 hp/lb air/sec.

4. Fuel supplied to direct contact boiler 8 is 0.0575 lb/lb air/sec and the water supplied is 0.874 lb/lb air/sec at 700.degree. F. Total heat input rate is 1110 Btu/Sec.

5. The steam-gases mixture leaves the direct contact boiler 8 at 1600.degree. F. and 3500 psia where it enters the first stage turbine 9. A 100 psia pressure loss in the boiler is allowed. The various amount of bleed gases for the heaters are shown in FIG. 1. The gases leave the second stage expansion turbine at 10a at 16.7 psia and 238.degree. F. The two stage turbines 9 and 10 produce 1266 hp/lb air/sec. The various coupling of turbines (9, 10, and 12) and compressors (1 and 4) for driving purpose are optional.

6. Heat exchange in Freon boiler steam condenser (11) is 574 Btu/sec.

7. Power output of Freon turbine (12) is 144 hp/lb air/sec.

8. Heat rejected in Freon condenser (13) is 476 But/sec. This engine has a thermal efficiency of 57% and net power output of 902 hp/lb air/sec.

9. Overall cycle efficiency is 57% at 1600.degree. F. (maximum) generator discharge.

Thus in consideration of the above disclosure it is apparent that there has been provided in accordance with the invention disclosed, a steam injected turbine powered generating system incorporating a high pressure direct fired steam generator providing improved efficiency and operating within temperature limits of available technology. The system disclosed, therefore, fully satisfies the objects aims and advantages set forth above. While the steam injected turbine system has been described here in conjunction with a specific embodiment thereof, it is evident that many alternatives modifications and variations will be apparent to those skillful in the art when viewed in the light of the foregoing description. Accordingly, it is intended to embrace any and all such alternatives, modification and variations as fall within the spirit and broad scope of the appended claim.

Claims

1. In a hybrid steam/gas turbine power plant of the type utilizing a direct fired steam generator supplying high pressure steam and combustion products at an outlet for operating a drive turbine, the improvement comprising:

a direct fired steam generator having fuel, combustion air, and feed water inlets, and an outlet delivering combined steam and combustion gases as high pressure and temperature exhaust products;

a drive turbine having an inlet and outlet, a fluid operated drive stage and a shaft coupled second compressor stage said compressor stage having an air inlet and an air outlet for supplying pressured combustion air to said generator;

a first compressor having an air inlet and outlet, said outlet supplying pressurized combustion air to said second compressor inlet;

means flow communicating said generator exhaust products to said turbine inlet for operating said drive stage;

means in said drive turbine, extracting a plurality of turbine drive stage fluid discharge products at a plurality of first temperatures and pressures, respectively;

means fluid communicating said drive turbine fluid discharge products to a plurality of predetermined locations;

first heat exchange means in at least one of said locations having a drive turbine discharge product inlet and an outlet, a cooling fluid inlet and outlet, and fluid impermeable means therebetween; and,

means supplying steam generator feedwater as cooling fluid to said first heat exchanger inlet, said cooling fluid inflow and outflow having second and third inlet and outlet temperatures respectively, and means limiting cooling fluid outflow at said third temperature and pressure corresponding to fluid saturation at said first drive turbine fluid discharge first temperature and pressure temperature;

second heat exchange means intermediate said first compressor and second compressor means, for cooling said generator combustion air having an air inlet and outlet, said air inlet in fluid communication with said first compressor air outlet, a fluid inlet and outlet and fluid isolating means therebetween;

means supplying said feedwater as cooling fluid to said second exchanger fluid inlet, for reducing said generator combustion air temperature thereby increasing generator exhaust product at increased pressure and temperature;

whereby said generator exhaust product is increased and cooling fluid temperature does not exceed saturation providing turbine operation at increased efficiency.

2. The power plant of claim 1 further comprising:

means controlling said cooling fluid flow through said first heat exchange means;

a first fluid expansion turbine for extracting shaft work from said turbine discharge fluids;

a fluid inlet and separate liquid and vapor outlets on said expansion turbine;

means admitting at least one of said drive turbine discharge means to said expansion turbine inlet;

means admitting said expansion turbine liquid exhaust to said first heat exchanger turbine discharge inlet; and

a tertiary fluid loop thermally coupled to said cooling fluid, said tertiary loop fluid operating at a saturation temperature and pressure substantially lower than that of said cooling liquid;

wherein heat recovered from said drive turbine exhaust liquid is transferred to said liquid cooling loop at temperatures below saturation of said tertiary liquid.

3. The power plant of claim 2 further comprising;

means condensing said first expansion turbine vapor exhaust having tertiary fluid and drive turbine inlets and outlets, thereby recovering vapor exhaust heat and generator feedwater;

means, in said condensing means, transferring said vapor exhaust heat to said tertiary fluid, said exhaust heat generating tertiary fluid vapor at a fourth temperature and pressure.

4. The power plant of claim 3 further comprising:

a second combustion air compressor shaft coupled to said first fluid expansion turbine said compressor having an atmospheric air inlet and an outlet;

a second fluid expansion turbine, for extracting shaft work from said tertiary fluid vapor;

means on said second expansion turbine admitting said tertiary fluid at said fourth temperature and pressure and discharging tertiary fluid and vapor at a fifth temperature and pressure;

a second heat exhanger intermediate said second combustion air compressor outlet and first combustion air compressor inlet, having a combustion air inlet and outlet tertiary fluid and vapor inlet and outlet and fluid isolating means therebetween;

means fluid communicating said heat exchanger air inlet and second compressor air inlet;

means fluid communicating said heat exchanger air outlet and first compressor air inlet;

means fluid communicating said second expansion turbine discharge and second heat exchanger tertiary fluid/vapor inlet;

means fluid communicating said exchanger tertiary fluid outlet and condensing means heat transferring means;

whereby said tertiary fluid recovers first expansion turbine exhaust heat at temperatures below said turbine exhaust.

5. A method extending the life of a turbine utilized in a hybrid steam/gas turbine power plant of the type utilizing a direct fired steam generator for supplying steam and combustion products to the inlet of a drive turbine having a shaft coupled compressor stage comprising the steps of:

Operating a direct fired steam generator having feedwater, combustion air and fuel inlets, and an outlet delivering exhaust steam and combustion products for operating a drive turbine at a predetermined pressure;

Providing a plurality of pressure and temperature staged exhaust discharges in said drive turbine;

transferring heat, from said turbine exhausts to said generator feedwater; thereby heating said feedwater;

limiting said feedwater heating to saturation temperatures and pressures of said feedwater;

compressing atmospheric air in said compressor to a predetermined pressure and temperature for use as generator combustion air;

supplying said combustion air, feedwater, and fuel to said generator inlets;

cooling said combustion air by transferring heat to said steam generator feedwater;

establishing a combination of said steam generator fuel, feedwater and combustion air flows such that said steam generator exhaust temperatures and pressure does not exceed a predetermined value.

6. The method of claim 5 wherein said establishing step includes the step of limiting the steam generator exhaust to a critical value of 1600.degree. F.

7. The method of claim 6 wherein said establishing step includes the step of limiting the steam generator exhaust pressure to a critical value of 3000 lbs. per square inch.

8. The method of claim 6 further comprising the steps of:

operating a first expansion turbine from at least one of said drive turbine discharges;

establishing a fluid discharge in said expansion turbine;

condensing said discharged fluid thereby generating heat and condensed generator feedwater;

establishing a tertiary fluid heat exchange loop, said tertiary fluid having saturation temperature and pressure substantially less than said expansion turbine discharge;

transferring said condensed feedwater heat to said tertiary fluid, thereby generating tertiary fluid vapor;

driving a second expansion turbine with said tertiary vapor, thereby generating shaft work.